Ballast transformer system for lamps



Sept. 3, 1968 D. LovlNGr-:R ETAL 3,400,299

BALLAST TRANSFORMER SYSTEM FOR LAMPS 3 Sheets-Sheet 1 Filed Dec. 25, 1965 tar/ray- Sept 3, 1968 D. LOVINGER ETAL BALLAST TRANSPORT/[ER SYSTEM FOR LAMPS 3 Sheets-Sheet 2 Filed Dec. 23, 1965 D. LOVINGER ETAL4 3,400,299

BALLAST TRANSFORMER SYSTEM FOR LAMPS sept. 3,1968

3 Sheets-Sheet 5 Filed Dec. 23, 1965 /NSIJIA TIA/6 /NSI/zAr/Ne srv/Rava fer6 .to/uw r m alba Kw4 .u ww

United States Patent O 3,400,299 BALLAST TRANSFORMER SYSTEM FOR LAMPS Daniel Lovinger and Franklin P. Eppert, Danville, Ill.,

assignors to General Electric Company, a corporation of New York Filed Dec. 23, 1965, Ser. No. 515,898 2 Claims. (Cl. 315-97) ABSTRACT F THE DISCLOSURE A ballast for a fluorescent lamp including a magnetic core and primary, secondary and heater windings coupled thereto. A capacitor is provided and includes an electrically conductive case, two insulated terminals, at least three insulating strips and three conducting strips. One of the conducting strips is insulated from the other two by one of the insulating strips. The other two conducting strips are spaced lfrom each other in end-to-end relationship to thus provide two capacitors with a common conducting strip. The common conducting strip is electrically connected to one of the insulated terminals and one of the other two conducting strips is electrically connected to the other insulated terminal. 'Phe remaining conducting strip is'electrically connected to the case. One insulated terminal is connected to the secondary winding and the other is connected to the lamp while the case is connected to one of the heater windings.

The invention relates to ballast apparatus for fluorescent la-mps, and particularly to such ballast apparatus having an improved capacitor circuit arrangement.

Fluorescent lamp ballasts are generally placed in a case 'with one or more capacitors to provide balla-sting, or power factor correction, or starting, or interference suppression, or for any combination of these functions. Previously, the best construction of fluorescent lamp ballasts using such capacitors represented a compromise. For example, it is diflicult to locate all of the insulated terminals of the capacitor at the optimum location from the standpoint of good capacitor construction and from the standpoint of good ballast construction. This is particularly true of wound capacitors which generally comprise two or more elongated strips of conductive material each separated iby an elongated strip or strips of insulating or dielectric material. The strips are wound and housed in a metallic can or case with the conductive strips insulated from the can. A plurality of such wound capacitors can -be provided in a single can by the use of additional conductive and insulating strips. Previously all of the conductive lstrips have been connected to insulated terminals on the can Afor connection to the re-mainder of the 'ballast. If the insulated terminals are placed for easy connection to the conductive strips, then the terminals may 'be difiicult to insulate from the ballast components, or connections between the ballast components and the terminals may be diflicult or expensive, or automatic connection-s between the ballast components `an-d the terminals may be impossible.

Accordingly, an object of the invention is to provide an improved fluorescent lamp ballast having one or more capacitors housed in a single can, one capacitor plate being connected to the can which serves as the terminal for that one capacitor plate.

Another object of the invention is to provide a novel fluorescent lamp .ballast having an improved capacitor circuit arrangement.

Another object of the invention is to provide an improved lluorescent lamp ballast apparatus in -which the capacitor is housed in a can that serves as one terminal for connection to other elements of the ballast.

Another object of the in-vention is to provide an improved lluorescent lamp ballast apparatus, having one or more wound capacitors, which is more yeasily constructed and assembled by having one terminal of the capacitor connected to the capacitor can.

Briey, these and other objects are achieved in accordance with the invention by an improved ballast apparatus having a shell-type core with a number of windings. The core and windings are mounted in a ballast case along with capacitor or capacitors which are to be provided in the ballast case. Connections between the core windings or other 'ballast elements and one of the capacitors is facilitated by having a terminal of that capacitor terminated on the capacitor can. Termination of the terminal on the can is preferably made Iwith a wound capacitor in which a conductive tab is inserted in contact with one conductive strip of the capacitor. The exposed part of the tab is positioned so that it contacts an inner face of the capacitor can with the wound strips placed in the can. This contact may be only trictional, or may be by some other means such as welding or soldering. With the tab lconnected to the can, the can serves as one terminal for an easy and i-mproved connection to the other elements of the fluorescent lamp ballast apparatus.

The invention is particularly pointed out in the claims. The invention may be better understood from the following description given in connection with the accompanying drawing, in which:

FIGURE 1 shows a schematic diagram of an improved lluorescent lamp ballast in accordance with the invention and having capacitors structurally represented;

FIGURES 2 and 3 show the physical arrangement of the ballast of FIGURE l;

FIGURE 4 shows a more detailed view of the structure of the capacitors used in the ballast of FIGURE 1 in accordance with the invention;

FIGURE 5 shows an exploded view in perspective of strips forming two wound capacitors for use in an improved ballast in accordance with the invention;

FIGURE 6 shows a more detailed View of the structure ofthe capacitors of FIGURE 5; and

FIGURE 7 shows a sectional view of the capacitors of FIGURES 5 and 6 in assembled form.

FIGURE l shows a schematic diagram of an improved fluorescent lamp ballast constructed in accordance with the invention and housed in a suitable case indicated by the dashed line 52. The ballast shown in FIGURE 1 is intended to operate two fluorescent lamps 1 and 2 from a source of alternating current such as volts, 60 cycles. The ballast includes a primary winding A, a secondary winding D, and three heater windings G, H, and J coupled to a common core. The core is designed to provide some leakage reactance between the primary winding A and the secondary winding D. The winding terminals are indicated by the letters S and F for start and nish respectively, followed by the winding letter. For example, the start terminal of the primary winding A is indicated by the legend SA, and the finish terminal of the primary winding A is indicated by the legend FA. The primary winding A and one heater winding I are serially connected between two input leads which are provided for connection to the alternating current source. The start terminal SD of the secondary winding D is connected to the primary winding A as an autotransformer, as indicated by the polarity dots, to provide sufficient voltage for the fluorescent lamps.

As will be explained in more detail hereinafter, three capacitors are provided in the improved ballast, these being a ballast capacitor, a tuning capacitor, and a start capacitor. The ballast and tuning capacitors have one plate terminated on respective insulted terminals as indicated, and the start capacitor has one plate terminated on the capacitor case as indicated. The three capacitors have a common plate terminated on an insulated terminal as indicated. The capacitor structure shown in FIGURE l comprises plates or conducting strips which are separated by insulating strips, and which are wound to form a cornpact structure. The finish terminal FD of the secondary winding D is connected to the ballast capacitor terminal. The common capacitor terminal is connected to one cathode or heating element of the lamp 2. The other cathode of the lamp 2 is connected to one cathode of the lamp 1. The other cathode of the lamp 1 is connected to the heater winding I to complete the lamp circuit. The heater winding H is connected to the cathode of the lamp 2, and the heater winding G is connected to the common cathodes of the lamp 2 and the lamp 1. An inductance 50 is connected between the start terminal SD of the secondary winding D and the tuning capacitor terminal by an inductance terminal L. This inductance 50 and tuning capacitor are preferably tuned to 420 cycles under open circuit or unloaded conditions to increase the RMS voltage under start and thereby permit the number of secondary winding turns to be reduced and also to provide an improved lamp current waveform. This feature is described in a U.S. Patent No. 3,225,255, issued Dec. 21, 1965 to Roger E. Hume and assigned to the General Electric Company, assignee of the present invention. One terminal of the heater winding G is connected to the start capacitor terminal. While the start capacitor was selected to have its terminal connected to the case of the wound capacitor, one of the other capacitors can have its terminal connected to the case instead.

FIGURE 2 shows a plan view of the physical arrangement of the ballast shown schematically and the capacitors shown structurally in FIGURE 1. The ballast elements are housed in a case 52 (corresponding to the dashed line 52 in FIGURE l) with the tuning inductor 50 at the left end, the primary, secondary and heater windings on a shell-type core generally in the middle, and the capacitors at the right end. After the ballast components are assembled and connected, they are usually embedded in a suitable material such as an asphalt compound, and a covering placed on the case 52. The winding, capacitor, and inductance terminals of FIGURE 1 are also indicated in FIGURE 2 with corresponding letters. In FIGURE 2, it will be seen how a connection between the start terminal SG of the ballast heater winding G and the capacitor case can be easily made to connect a capacitor (in this case the start capacitor) in the ballast. This connection can be made after the various components are inserted into the case 52 without the necessity of the additional terminal at the end of the capacitor case, or, without the necessity of an additional tubular capacitor with its attendant leads and connections. The capacitor case is suitably insulated from the case 52 by a sheet of insulating material 60 wrapped around the capacitor case. FIGURE 3 shows a detailed View, with the material 60 partially broken away, of the connection between the capacitor case and the start terminal SG.

An end or edge view of the three capacitors used in the ballast of FIGURES l, 2, and 3 are shown in greater detail in FIGURE 4. The three capacitors are actually wound in a spiral and placed in a case, but are shown unwound in FIGURE 4 for clarity and explanation. The capacitors are formed of three foil strips 40b, 401, 40s which are placed between an insulating strip 12 on one side and two insulating strips 18 (for added insulation) on the other side. The foil strip 40h is connected through a tab to the ballast terminal which may be mounted on the top of the capacitor case. The foil strip 40t is connected through a tab to the tuning terminal T (FIG- URE 2) which may also be mounted on the top of the capacitor case. And the foil strip 40s is connected through a tab to the case (start) capacitor. A foil strip 42 is positioned on the other side of the insulating strips 18 from the strips 40h, 40t, 40s to provide a common plate for the various capacitors. An insulating strip 10 is placed on the outer side of the foil strip 42 so that all foil strips are insulated on both sides. The strip 42 is connected through a tab to the common terminal which may be mounted on top of the capacitor case. The three capacitors shown in FIGURE 4 provide the functions of ballasting, tuning, and starting in the fluorescent lamp ballast of FIGURES l, 2, and 3. The ballast is more easily constructed and assembled because one ballast connection can be made directly to the capacitor case at any suitable point. In the example selected, the case connection is provided for the start capacitor, but the case connection can be provided for any one of the capacitors. During assembly, it is much easier for an operator to make a connection to the case (at almost any location) than to an insulated terminal (at a substantially fixed location).

While FIGURES 1, 2, 3, and 4 show the ballast of the invention incorporating a capacitor case with three capacitors, the case may contain only one capacitor, or two capacitors, or any number of capacitors. The invention provides the advantage of one ballast connection being made to the capacitor case. Further details of the capacitor construction are shown in FIGURES 5, 6, and 7. In these figures, a capacitor case with two capacitors, such as a ballast capacitor and a start capacitor, has been illustrated for purposes of explanation. FIGURE 5 shows a perspective view of the capacitors. The capacitors are formed by two elongated insulating or dielectric ribbons or strips 10, 12; three elongated conducting or foil ribbons or strips 14, 16a (not visible in FIGURE 5), 16b between the insulating strips 10, 12; and two elongated insulating or dielectric ribbons or strips 18 between the foil strip 14 and the foil strips 16a, 1611. The foil strips 14, 16a, 16h are preferably made slightly narrower than the insulating strips 10, 12, 18 to prevent the edges of the foil strips 14, 16a, 1Gb from being short circuited or improperly contacted. The insulating strips 10, 12, 18 may be made of kraft paper, and the foil strips 14, 16a, 16b may be made of aluminum. As shown in FIGURE 5, the insulating and foil strips are alternated so that the foil strip 14 and the foil strips 16a, 16b have insulating strips on each side or face. Two insulating strips 18 are used between the foil strip 14 and the foil strips 16a, 16b for added insulation, but only one such strip may be used. The strips are wound together for a sufficient length to provide the desired capacity which varies as a function of the area of the foil strips 14, 16a, 1Gb. The strips are wound about their width in a circular fashion, or in a generally elliptical fashion as shown in FIGURE 5.

In the capacitor of FIGURE 5, the two foil strips 16a, 16b form two capacitor plates with respect to the foil strip 14 which forms a common capacitor plate. This is shown by FIGURE 6 which represents an end or edge view along the length of the strips in their unwound condition. During the winding of the strips and at some appropriate point along their length, a terminal tab is connected to the first foil strip 16a. This terminal tab contacts or engages the foil strip 16a, and may be held by friction and pressure of subsequent strip layers, or may be fastened to the foil strip 16a by suitable means such as welding, riveting, or crimping. The terminal tab may be similar to the case tab which will be described subsequently. At some distance from the terminal tab, the rst foil strip 16a ends and the second foil strip 16b begins. A common tab is connected to the foil strip 14 at some appropriate point along its length in a manner which may be similar to the connection for the terminal tab. The common tab and the terminal tab are respectively brought out and connected to terminals which are supported on but insulated from a top 20 for the capacitor can or case 26. The top 20 is preferably made of a metallic material such as aluminum, and is covered with a rst insulating piece 22 of kraft board which prevents the foil strips from contacting the top 20. A second insulating piece 24 of phenolic may be placed beneath the piece 22 for added insulation for the capacitor. The common tab and the terminal tab are fastened to these terminals by any suitable means such as Welding, soldering or riveting. The capacitor case 26 is metallic and preferably made of aluminum or some metal that is easily stamped or formed into shape. The case 26 has a shape which conforms to the shape of the wound strips. The bottom of the case 26 is closed, and the top of the case 26 has an opening with a rim or lip to which the top 2t) can be fastened to provide a sealed housing or case for the capacitors.

To provide the improved -ballast construction in accordance with the invention, the second foil strip 16b is connected to the case 26 through a case tab 28 and a tab strip 30. The case tab 2S and the tap strip 30 are metallic strips of aluminum or other metal that are `fastened together, preferably by small rivets. The tab strip 30 is laid on the second foil strip 16b near its outer end so that the case tab 28 can be easily folded over and down along the wound strips. The case tab 28 and the tab strip 30 are held in good contact with the second foil strip 16b by the pressure of additional layers of strips, but further or other types of fastening, such as welding, riveting, or crimping, may be provided. After the winding of the strips is completed, the common tab and the terminal tab are connected to their terminals in the top The case tab 2S is then bent over the upper edges of the outer layers of strips and down against the side of the insulating strip 12 which will be on the outside. The assembly is then placed in the capacitor case 26. Normally, the case tab 28 will make good contact with the inner surface of the capacitor case 26. However, additional contact pressure may be provided by the flattening or depressing of opposite walls of the case 26. This is normally done to provide a stable magnitude of capacity. Thus, a first capacitor is provided between the terminal tab and the common tab, and :a second capacitor is provided between the case tab and the common tab. The capacitor case 26 may, if necessary, be insulated by some suitable means such as a film of plastic wrapped around the case 26. Or, the capacitor may be embedded in an insulating material.

FIGURE 7 shows a transverse cross sectional View of an assembled capacitor such as shown in FIGURES 5 and 6. FIGURE 7 shows how the terminal and common tabs are insulated from the top 20 and connected to the external terminals. FIGURE 7 also shows how the case tab 28 is folded over and down alongside the wound strips so as to come in firm engagement or contact with the inner surface of the case 26. External connection to the case tab 28 (and its capacitor lplate) may be made at any point on the case 26.

The invention provides a new and improved ballast in `which one connection to a capacitor is made on a metallic capacitor case. This -connection may be made at any point on the case. Such a ballast is advantageous because the utilization of the capacitor case as a terminal provides a good compromise in the manufacture of the capacitor and in the manufacture of the ballast using the capacitor. This good compromise yresults from the relative ease with which one capacitor plate is connected to the case and the relative ease with which a ballast element is connected to the case.

It will thus been seen that the invention provides an improved ballast having one connection made to the ballast capacitor case. The capacitor case terminal penmits an added capacitor to be housed in the capacitor case because the added capacitor terminal need not Ibe brought out on an insulated terminal. An added insulated terminal may be difficult to provide, and is difficult to connect into a -ballast because of space limitations and assembly techniques. Thus, the ballast connected to a capacitor case terminal in accordance with the invention facilitates assembly of the -ballast apparatus. Persons skilled in the art will appreciate that modifications iof the invention may be made. For example, any one of the ballast capacitors may be connected to the case. The connection of the strip to the case may be modified to suit manufacturing techniques. And the connection between the ballast element and the capacitor case may be made at any stage of the ballast construction. Therefore, while the invention has been described with reference to particular embodiments, it is to be understood that modifications may be made without 4departing from the spirit of the invention or from the scope of the claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A ballast for a fiuorescent lamp comprising: a ballast housing; a magnetic core having a primary winding, a secondary winding, and a plurality of heater windings coupled thereto and positioned within said ballast hous ing; a ballast capacitor positioned Within said ballast housing and comprising an electrically conductive case, first and second terminals insulated from said case, at least first, second and third insulating strips, first, second and third conducting strips, said insulating strips and said conducting strips being Wound so that at least said first insulating strip insulates said first and second conducting strips from said third conducting strip, said rst and second conducting strips being spaced from each other in an end-to-end relationship, said second and third insulating strips insulating said first, second and third conducting strips from said case, means electrically connecting said first conducting strip to said first terminal, means electrically lconnecting said second conducting strip to said case, means electrically connecting said third conductive strip to said second terminal, said insulating strips and said conducting strips being positioned within said case; means electrically connecting said first terminal to said secondary winding; means to electrically connect said second tenminal to the lamp; and, means electrically connecting said case to at least one of said heater windings.

2. The invention `of claim 1 wherein said means electrically connecting said second conducting strip to said case comprises a conductive tab electrically connected to said second conducting strip, extending out beyond said insulating strips and bent over to be sandwiched between said case and the outermost insulating strip.

References Cited UNITED STATES PATENTS 3,080,503 3/1963 Brooks 315-187 3,116,437 12/196-3 Harvey 315-123 3,163,807 12/1964 Linderholm 317-260 3,192,457 6/1965 Crockett et :al 317-260 3,225,255 12/1965 AHume 315--232 MILTON O. HIRSHFIE-LD, Primary Examiner.

W. E. RAY, Assistant Examiner. 

